1. Field of the Invention
The present invention relates to the telecommunication field and in particular to a method and network element for transporting Ethernet frames over a transport SDH/SONET network. Still more in particular, the present invention relates to a method and network element allowing the retransmission of Ethernet frames over a SDH/SONET network.
As it is known, traffic generated by an Ethernet apparatus is characterized by discontinuities, namely there are periods with a more or less constant sending rate of Ethernet packets and periods during which a rather long time is provided between a received Ethernet frame and the next one. Such unstable/inconstant traffic is generally termed “bursty”. On the contrary, SDH or SONET traffic is characterized by a constant sending/receiving rate. In other words, any network element of a transport SDH/SONET network sends corresponding frames with a regular and constant rate. Furthermore, Ethernet frames do not have a fixed length/size but only a maximum size (1518 bytes).
It is easy to understand that these discrepancies result in a highly difficult interfacing of two technologies having different natures/characteristics.
2. Description of the Prior Art
An already available solution to the above problem allows the mapping of Ethernet frames into SDH/SONET Virtual Containers as a transparent tributary; all incoming bits are transported to the output interface with the related timing information (frequency for recovering the proper bit rate at the reception side). Within the SDH/SONET payload also the dead times between a received Ethernet frame and the following one are mapped.
The general problem of transporting Ethernet frames over a SONET/SDH transport network is presently solved through SONET/SDH virtual concatenation.
Sometimes, Ethernet frames could become lost in the network for different reasons, for instance because of a fail in the network. At present, the step of Ethernet re-transmission is managed at a higher layer level but, due to such a higher layer management, the re-transmission of Ethernet frames is a rather long procedure and it could not be performed in an efficient manner.
Thus, there still remain the problem of how to perform a low-layer and fast retransmission of Ethernet frames that have been lost along their transport over the SDH/SONET network.